Method of making a heat developable sheet containing mercury lens

ABSTRACT

A LIGHT SENSITIVE HEAT-DEVELOPABLE SHEET MATERIAL CONTAINING SILVER HALIDE AS A CATALYST PROGENITOR FOR THE OXIDATION-REDUCTION REACTION OF IMAGE-FORMING REACTANTS COMPRISING SILVER SOAP AND REDUCING AGENT INCLUDES A SOURCE OF MERCURY ION AND RESTRICTED AMOUNTS OF PHTHALAZININE, TO PROVIDE A SHEET WHICH SHOWS A NEGATIVE SLOPE IN THE D LOG E CURVE AND WHICH PRODUCES A DIRECT POSITIVE WHEN EXPOSED TO A LIGHT IMAGE OF A POSITIVE ORIGINAL AND THEN SUBJECTED TO MINIMUM HEATING REQUIRED TO PRODUCE MAXIMUM USEFUL AT UNEXPOSED AREAS.

June '29, 1971 n, o s 3,589,901

1 METHOD OF MAKING A HEAT DEVELOPABLE SHEET CONTAINING MERCURYLENS Fil d Feb. 25, 1958 I ZShQBtS-SHOGT. 1

10 EXPOJ'URE X q EXAMPLE 6 Q I? 5 Jim/v0 5/1557 2 25 (u/varpasmj 40. Ex ose/R5 I N VliN UR. 7710/14/45 0. A yam- BY M ,JZZMVMM United States Patent 3,589,901 METHOD OF MAKING A HEAT DEVELOPABLE SHEET CONTAINING MERCURY LENS Thomas D. Lyons, St. Paul, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul,

Minn.

Filed Feb. 28, 1968, Ser. No. 708,988 Int. Cl. G03c 5/24, 1/08 U.S. Cl. 9664 6 Claims ABSTRACT OF THE DISCLOSURE A light sensitive heat-developable sheet material containing silver halide as a catalyst progenitor for the oxidation-reduction reaction of image-forming reactants comprising silver soap and reducing agent includes a source of mercury ion and restricted amounts of phthalazinone, to provide a sheet which shows a negative slope in the D log E curve and which produces a direct positive when exposed to a light image of a positive original and then subjected to minimum heating required to produce maximum useful density at unexposed areas.

This invention relates to the recording of light-images on long chain fatty acid silver soap light-sensitive heatdevelopable film or sheet materials, and has particular reference to the making of positive records in which the relative densities of image and background areas are the same in the record and in the original from which the light-image is taken.

The process has particular utility in such operations as the duplicating of records in microfilm or X-ray film and in the copying of printed documents, line drawings, continuous-tone photographic positive transparencies and other graphic originals. Only a limited exposure is required. The sheet materials are stable on prolonged storage and produce stable long-lasting records. The products of the invention may be supplied as coatings on any desired substrate but are ordinarily supplied as opaque coated papers or transparent coated films.

In U.S. application Ser. No. 693,714 filed Dec. 27, 1967, now U.S. Pat. No. 3,457,075, there is described a light-sensitive heat-developable sheet material containing a photosensitive silver halide in catalytic association with an image-forming oxidation-reduction reaction mixture of organic silver salt and reducing agent. Exposure of the sheet to a light-image results in the formation at the light-exposed areas of a catalyst which accelerates the heat-reaction of the silver salt mixture, the latter then on subsequent heating undergoing accelerated reaction at the catalyzed areas to develop "a corresponding visible image.

The addition of mercury andphthalazinone to such light-sensitive heat-developable sheet materials is described in U.S. application Ser. No. 708,989 filed on even date herewith. That application describes improvements in stability and photographic speed, but the formulas and processes described result in the formation of reversal images, i.e. wherein darkening occurs preferentially at the light struck areas.

The present invention likewise involves the incorportion of phthalazinone and of a source of mercuric ion in the dry silver sensitive sheet coatings, but in specific defined amounts and proportions to provide the unique results herein described.

The present invention also involves certain techniques and procedures which are essential to the successful application of the specifically defined compositions and coatings in obtaining the different and highly useful results here made possible.

The sensitometric characteristics of light-sensitive ice image-forming materials are conventionally reported in terms of the D log E curve, obtained by plotting the optical density of the image produced on development, under fixed conditions, of portions of the sheet exposed sensitometrically, i.e. to increasing amounts of radiant energy. The ability of the sensitive sheet to record lightimages to which it is exposed is ordinarily shown by a positive slope of the D log E curve over the significant portion of the exposure range.

Surprisingly, it has now been found that with certain formulations it is possible to provide sensitive sheets whose D log E curve shows a negative slope. Such materials are capable of producing direct positive copies by heat-development after exposure to a light-image, the light-struck areas remaining substantially undarkened in the copy. A critical feature of the compositions is that the molar ratio of phthalazinone to mercury must not exceed about eight. Proportions of phthalazinone within this general range, while resulting in the formation of reversal copies under some exposure and development conditions, are found under other and dilferent conditions to permit the preparation of direct positives. The source of mercuric ion should be present in an amount of from about .0004 to at least about 0.1 or 0.15 mol of mercury per mol of silver. Within these general ranges, further selection must be made depending on the particular reducing agent and other variations, the composition in all cases being selected to provide the required negative slope in the D log E curve. Development is by heating to the minimum extent required to produce maximum useful density in the unexposed areas.

Another surprising feature of the present invention is the ability to increase the sensitivity of the direct positive sheet by the incorporation of spectrally sensitizing dyes. Orders-of-magnitude reduction in required time of exposure may be achieved by the inclusion of such materials. Another feature is the ability of the image-exposed direct positive acting sheet material to induce formation of a duplicate image on a further sheet of the sensitive material during development. Thus two copies may be produced simultaneously with but a single exposure; and the second copy is found to possess a brighter background than that of the exposed sheet.

The mercuric ion may be introduced in any desired manner. A mercuric compound may be added to the coating composition containing either the organic silver salt, or the reducing agent, or both; or it may be applied as a separate coating. It has been found particularly convenient to introduce the mercuric ion in the form of mercuric halide under conditions which permit the halide ion to react with a small proportion of the organic silver salt to form the required photosensitive silver halide, the latter remaining in catalytic proximity with the remainder of the silver salt. Where other sources of halide ion are provided, the mercuric ion may be introduced in the form of compounds of anions other than the halide, for example acetate, behenate, benzoate, bromate, chromate, citrate, chloranilate, iodate, lactate, nitrate, oxalate, phthalate, salicylate, succinate, sulfate or as mercury compounds of hexamethylenetetramine, pentachlorophenol, or phthalazinone. Any compound capable of providing mercuric ions in the system employed as operable in the practice of the invention; but compounds of extremely low solubility, or dark color, or whose anions have a deleterious effect, such for example as mercuric sulfide or thiocyanate, will ordinarily be avoided.

Silver behenate half soap is a mixture of equimolar proportions of silver behenate and behenic acid, obtained by precipitation with silver nitrate and nitric acid from the sodium salt of commercial behenic acid. Other ratios of silver salt and free acid may be used, or the free acid may be omitted, particularly where transparency is desired. Silver salts of other long chain fatty acids, e.g. silver stearate or silver myristrate, may be used.

The sheet material of this invention contains as the reducing agent for the silver soap material one or more sterically hindered normally solid ortho-substituted, and usually o-alkyl-substituted, phenolic reducing agent. These materials in the absence of phthalazinone or the like react only with difficulty with silver behenate. As an example, the two materials may be suspended together in an organic solvent or in dry powdered form for many days without any evidence of inter-reaction. If mixed with a polymeric binder in a thin coating on a paper, the two are found to react only at relatively high temperatures of the order of 150 C. or higher, and even then with the formation of low-density yellowish coloration rather then the black dense appearance normally ascribed to the silver image formed on reduction of silver behenate. In the presence of the phthalazinone, however, the combination of silver behenate and reducing agent is found to produce dense black image areas, e.g. when heated to about 140 C.

Examples of solid water-insoluble ortho-substituted phenols which have been shown to be useful in these compositions include a number of compounds commercially available as anti-oxidant or preservative materials and identifiable as: 2,S-dihydroxyacetophenone; bis (2- hydroxy 3 tertiarybutyl methylphenyl) methane; bis (2 hydroxy 3,5 di t butylphenyl) methane; 2,4,4- trimethylpentyl bis (2 hydroxy 3,5 dimethylphenyl) methane; 4,4'-methylenebis (3 methyl 5 tbutylphenol); bis (Ii-methyl 4 hydroxy 5 t butylphenyl) sulfide; 4,4-methylenebis (2,6-di-t-butylphenol); 2,2 methylenebis (2 t butyl 4 ethylphenol; 3,5- di t butyl 4 hydroxybenzyl dimethylamine; 2,6- methylene-bis (2-hydroxy 3 t butyl-5-methylphenyl)- 4 methyl phenol; ,0! (3,5 di t butyl 4 hydroxyphenyl dimethylether; and 3,3',5,5' tetra t butyl-4,4'- dihydroxybiphenyl.

The drawing illustrates typical D log E curves obtained with the sensitive sheet materials of the several specific examples as indicated on the several figures.

The following examples will serve further to illustrate but not to limit the invention.

EXAMPLE 1 Composition A:

Silver behenate full soapg. Ethyl acetate-90 g. Mercuric bromide0.4 g. 0.05% dye solution4 ml. solution polyvinyl butyral-42 g.

The dye is 3-allyl-5-[3-ethyl-(2 naphthoxazoylidene) ethylidene]-1-phenyl-2-thiohydantoin, dissolved in chloroform. The polyvinyl butyral is non-tacky in thin films at 150 C.; it is dissolved in ethyl acetate.

Composition B:

Cellulose acetate butyrate (alcohol soluble) Phthalazinone a, x'- 3,5 -di-t-butyl-4-hydroxyphenyl) dimethyl ether Mixture of methyl alcoholzacetone, 4:1 by

volume 22.5

4 developed by heating at that temperature for 10 seconds. The resulting D log E curve shows a positive slope.

A further portion is heated for 10 seconds at somewhat higher temperatures, but not above the temperature at which the sheet first shows evidence of charring, blistering, offsetting or similar destructive influence, to determine the minimum temperature required to produce the maximum useful density; and this minimum heat input is employed to develop another sensitometrically exposed portion. The D log E curve obtained with this second portion is found to exhibit a negative slope followed almost immediately by an extended positive slope. Within the critical exposure time and under the critical heating conditions involved in producing such negative slope there may be obtained a direct positive, the unexposed portions adjacent this area of the wedge showing a higher density than the wedge-exposed portion.

Heating is preferably accomplished between heated smooth metal pressure-platens or by contact with a heated polished metal drum.

EXAMPLE 2 Silver behenate half soap-9.16 g.

Acetoneml.

Mercuric bromide-0.2 g.

12% solution of polyvinyl butyral in equal volumes of acetone and methanol-- g.

Phthalazinone.55 g.

2,6-bis(3 -t-butyl-2'-hydroxy-5'-methyl benzyl) -4- methylphenol-45 g.

.05 solution of 3-allyl-5-[ 3-ethyl-2-(3-H benzoxazoyldiene) ethyldene] l-methyl-Z- thiohydantoin in chloroform-2 ml.

Tetrachlorophthalic anhydride.0 l 5 g.

The half soap is first dispersed in the acetone by milling in a ball mill. The remaining components are added in the order given with minimum complete mixing and the com position is promptly coated through a 4 mil orifice on smlpolth paper previously lightly sized With polyvinyl alco 0 Portions of the coated sheet are heated at various temperatures without previous light exposure to determine the maximum available density. A portion is then exposed sensitometrically, i.e. through a wedge, and is heated at conditions of maximum density time and temperature. The resulting D log E curve shows a negative slope from a maximum density of 1.2 to a minimum of .16, or more than three times the difference obtained in Example 1.

EXAMPLE 3 G,. 15% suspension of silver behenate full soap 67 Mercuric bromide .4 15% solution of polyvinyl butyral 67 Phthalazinone .5 2,2'-methylene bis(4,6-di-t-butylphenyl) 4 The silver behenate is suspended in a mixture of equal volumes of toluene and methyl ethyl ketone and is passed through a homogenizer to give a non-settling gelatinous suspension. The polymeric material is dissolved in methyl ethyl ketone.

The composition is coated on 4 mil transparent Mylar polyester film at a wet thickness of 3 mils and is air dried.

Portions of the sheet are sensitomertically exposed and are then developed by heating for 10 seconds at 112 C., 0., 127 C. and 133 C. respectively. The first two show only a positive slope in the D log E curve, whereas the last two show a pronounced negative slope to the D log E curve, with a density differential maximum of 1.0 for curve No. 3 and 0.9 for curve No. 4.

A somewhat reduced but still useful density differential is obtained for the negative slope D log E curve using polyvinyl alcohol as the binder in place of polyvinylbutyral.

EXAMPLE 4 Composition A:

Silver soap suspension of Example 3-33.5 g. 2% solution of mercuric bromide in methanol5 ml. solution of polyvinyl butyral in 1:1 acetonemethanol25 g. Phthalazinone.25 g. Dye solution of Example 21 ml.

Composition B:

10% solution of cellulose acetate in acetone-25 g. 2,2-methylene bis (4-methyl-6-t-butylphenyl)l g. 1,1-bis (2-hydroxy-3,S-dimethylphenyl)-3,5,5-trimethyl hexanel g.

Transparent 3 mil Mylar polyester film is coated at 4 mils with composition A and, after drying, at 2 mils with composition B. Upon exposure to light from a tungsten source and through a wedge, and development for 10 seconds at 118 C., there is obtained a D log E curve showing a sharp negative slope followed by an almost equally sharp and somewhat extended positive slope, the curve indicating a density not greater than .2 between exposures of and 5 6 meter-candle-seconds.

Another example of the same sheet is exposed to a stream of electrons in an electron beam gun with accelerating potential of 20 kev. The strip is developed in a liquid fluorocarbon bath at 117 C. and for seconds. A clear transparent trace on a black background is obtained.

EXAMPLE 5 Composition A:

Silver behenate full soap10 g. Methyl ethyl ketone-100 ml. 2% solution mercuric bromide in methanol-10 ml. 25% solution polyvinyl butyral in methyl ethyl ketone-20 g. Composition B:

Acetone90 g. Methanoll0 g. Cellulose acetate-S g. Phthalazinone1 g. 2,2'-methylene-bis-(4,6-di-t-butylphenol)8 g.

Composition A is coated at an orifice of 4 mils on transparent Mylar polyester film, followed after drying by a 3 mil coating of composition B. The dried sheet is sensitometrically exposed and is developed for 10 seconds at 127 C. The D log E curve shows a negative slope from an initial density of almost 2 to a minimum density of .2 and the minimum density extends between exposures of 250 mcs. and 2500 mcs.

Although the amount of phthalazinone in this example appears from the concentrations and coating weights to be somewhat greater than eight mols per mol of mercury, its application in a separate layer reduces the etfective concentration to not more than the specified proportion, as evidenced by the negative slope of the D log E curve. The required proportionality of phthalazinone and mercury is determined from measurements made under equilibrium conditions.

In each of the foregoing examples, the negative slope characteristics of the D log E curve indicate the sheet to be capable of forming a direct positive record when exposed to a light image and then developed with minimum heating to produce maximum useful density at unexposed areas. It is therefore possible with these materials to produce duplicates of positive transparencies, printed documents and other originals, wherein the original and the copy will each consist of black or dark colored images on less dense, white or transparent backgrounds.

6 EXAMPLE 6 Silver behenate half soap9.66 g.

Acetone70 ml.

Mercuric bromide.l466 g.

11% solution of polyvinyl butyral in methanol and acetone g.

Phthalazinone-.6 g.

2,6 bis (3-t-butyl-2-hydroxy-5'-methylbenzyl)-4-methylphenol-4.75 g.

.05 dye solution of Example 2-2 ml.

Tetrachlorophthalic anhydride--.0l5 g.

The composition is coated at a thickness of 4 mils on smooth surfaced paper. A portion is exposed sensitometrically and is then placed in face-to-face contact with an unexposed portion of the same sheet, with a thin openmesh silk screen interposed between the coated surfaces. The composite is heated for 10 seconds at 126 C.

In each instance a large portion of the exposed area remains white, while the unexposed and lightly exposed areas become a dense brown-black. In both samples the D log E curve shows a negative slope.

What is claimed is as follows:

1. Method of making a direct positive recording from a light-image of a graphic original onto a light-sensitive heat-developable sheet material including photosensitive silver halide catalyst-forming means, heat-sensitive reactant image-forming means including an organic silver salt and a reducing agent the oxidation-reduction reaction of which to produce a visible change is accelerated by said catalyst, and a source of mercury ion in amount sufficient to impart a negative slope to the D log E curve; said method comprising exposing said sheet to said lightimage and then subjecting said sheet to minimum heat required to produce maximum useful density at unexposed areas.

2. Method of claim 1 wherein said sheet material includes phthalazinone and said reducing agent is an orthoalkyl-substituted phenolic reducing agent.

3. Method of claim 2 wherein said source of mercury ion is present in significant small amount up to about 0.15 mol per mol of silver.

4. Method of claim 3 wherein said phthalazinone is present in amount equivalent to not more than eight moles per mole of mercury.

5. Method of claim 1 wherein said sheet material includes a spectrally sensitizing dye for the silver halide.

6. Method of claim 2 wherein the exposed sheet is supported in close face-to-face relationship with an unexposed further sheet during heat development to provide on said further sheet an additional recording of said lightunage.

References Cited UNITED STATES PATENTS 3,218,166 1l/l965 Reitter 96-67 3,094,417 6/ 1963 Workman 9628 3,409,438 ll/ 1968 Lokken 9695 3,107,174 10/1963 Wartman ll736.2

OTHER REFERENCES Rose, The Condensed Chemical Dictionary, 1965, p. 810.

NORMAN G. TORCHIN, Primary Examiner E. C. KIMLIN, Assistant Examiner U.S. Cl. X.R. 96-402 

